At present, most lightning-proof power suppliers apply paralleled surge absorbers (voltage dependent resistor) (as shown in FIG. 1) to prevent surges, but the surge absorbers are restricted by their bearing capacity and unstable (such as respond slowly and will be invalid after withstanding several surge voltage). They usually can only withstand a surge voltage of 5-8 KV. And surge absorbers are encumbered by their large volume and high cost. Another way to prevent surge is to thicken the paint film of the primary coil of the transformer (shown as T in FIG. 1), wrap tape and sheath around the starting wire and the ending wire, for example. This method has complicated processes, high cost and poor reliability, and can only withstand 10 KV in the lightning test.